Cuffs are used in biomedical research and in clinical applications to surround and enclose internal body tissues, such as nerves, arteries, veins, muscles, tendons, ligaments, the oesophagus, intestines, fallopian tubes and other generally tubular internal organs. The functions of cuffs can include: chemically and/or electrically isolating selected tissues from surrounding tissues; supporting electrodes for electrically interacting with tissues inside the cuff; supporting tissues; administering drugs or chemicals to tissues within the cuff; and serving as a platform for physiological experiments.
A simple form of cuff that has been widely used in the prior art comprises a section of elastic tube that is slit longitudinally. These cuffs are implanted by separating the edges of the slit to expose the interior of the cuff, placing selected tissues on the cuff and then allowing the cuff to close around the selected tissues. The cuff is then tightly closed and sealed by tying sutures around the cuff at several places along its length. Cuffs of this nature are described in Hoffer, J. A. Techniques to study spinal-cord, peripheral nerve, and muscle activity in freely moving animals. in Neuromethods, Vol. 15: Neurophysiological Techniques: Application to Neural Systems, A. A. Boulton, G. B. Baker and C. H. Vanderwolf, editors. The Humana Press, pp. 65-145, 1990.
The prior art cuffs described above have several disadvantages. Some of these disadvantages arise from the use of sutures to close the cuff and are as follows:
1. Braided suture material, either absorbable or non-absorbable, can easily attract and retain contaminants. The presence of such contaminants can result in local foreign body reactions. PA1 2. Connective tissue can also grow on the sutures themselves and around the cuff, this can make removing the cuff difficult. PA1 3. Sutures of most suture materials have a limited lifetime within the fluid environment of the body and tend to break down at the location of the knots. If the suture material breaks down the cuff can open. Many suture materials can be reliably implanted for no more than a few months. PA1 4. A tradeoff must be made between increasing the number of closing sutures for a given length of nerve cuff to improve the electrical and mechanical isolation of the interior from the exterior, and decreasing the number of closing sutures to decrease the time, complexity, and skill required to implant the cuff on a nerve. PA1 (a) Providing a cuff of a size suitable to envelop the body tissue, the cuff comprising: a cuff member having a longitudinal slit in a wall thereof; at least one electrode disposed on an inner surface of the cuff member; a sealing closure comprising a plurality of interdigitated apertured members attached to the cuff member on alternate sides of the slit and a locking member capable of being inserted through apertures in the apertured members to lock the cuff closed; PA1 (b) Spreading sides of the slit apart and placing the cuff around the body tissue; PA1 (c) Sealing the cuff around the body tissue by interdigitating the apertured members; PA1 (d) Inserting the locking member through the apertures in the apertured members to lock the cuff closed; and PA1 (e) Extending an electrical connection to the electrode in the cuff.
Stainless steel sutures are easier to clean and should survive longer in the body than sutures of other materials. However, steel sutures are generally very stiff and difficult to tie into knots. Steel sutures are also thin and sharp and can easily cause damage by cutting through tissue and/or cuff materials during or after implantation of a cuff.
The cuffs described above also have disadvantages that arise from the use of a slit tube. In some cases, such cuffs can compress the tissues inside them and/or fail to provide an effective electrical and fluid seal around the enclosed tissues. These disadvantages are particularly significant for nerve cuffs. It is especially important in a nerve recording cuff that the cuff closure in the central portion of the cuff, where the recording electrodes are located, provide a good seal so that the cuff will provide good electrical isolation. One source of problems in prior art sutured cuffs is that if the sutures do not hold the cuff tightly closed then connective tissue tends to grow into the cuff through the open longitudinal slit. This reduces the electrical and mechanical isolation of the interior of the cuff. Breakdown of the cuff seal is therefore undesirable. Some prior cuffs have a thin, flexible flap on the outside of the cuff tubing which spans the longitudinal slit. The flap is held in place over the slit by sutures which encircle the cuff. If enough sutures are used to hold the flap down along the entire length of the cuff the flap can restrict fluid movement and tissue growth through the slit.
Another source of problems is that one edge of the longitudinal slit can slip radially inward with respect to the other edge of the slit. This reduces the volume inside the cuff and can consequently compress and damage the tissues in the lumen of the cuff. Where the cuff surrounds a nerve, severe damage can result if the edges of the cuff slip, as described, and the cuff squeezes the nerve.
An alternative cuff design is described by Naples et al. U.S. Pat. No. 4,602,624. The Naples et al. cuff is formed from laminated sheets of flexible, non-conducting, material. The laminated sheets are differentially stretched in the lamination process so that the cuff tends to cuff around itself, like a rolled up carpet. A special tool is preferably used to implant the cuff. When it is in place the cuff wraps around the enclosed tissues. The Naples et al. cuff does not require sutures to keep it closed.
For nerve recording cuff applications the Naples et al. cuff has the disadvantage that it does not always provide good enough electrical isolation of the interior of the cuff. Connective tissue may grow into the seam of the cuff from both the inside and the outside of the cuff. This connective tissue could eventually provide an unwanted shunting path for current flow and may even pry the cuff open.
The Naples et al. cuff has the further disadvantages that it typically requires a special tool for implantation and it may be difficult to implant. There is no simple method to open the cuff during surgical conditions. Implanting the Naples et al. cuff around a nerve or other delicate tissue can be risky. The cuff could seriously damage a nerve if it closes before the nerve is properly located. Another potential disadvantage of the Naples et al. cuff is that it may be difficult to remove without causing tissue damage.
Prior art cuffs, as described above, have been equipped with electrodes and used for interfacing with the nervous system by recording from or stimulating neural tissues. For example, implanted nerve cuffs are used to record nerve signals from peripheral nerves in animals in a wide range of experimental conditions. Nerve cuff electrodes have been used in stimulation systems with the goal of providing partial voluntary control of muscles that were paralyzed as a result of lesions caused by spinal cord injury, stroke, or other central neurological disorders. In some cases, partial motor function can be restored by stimulating motor neurons or muscles below the level of the lesion.
Recent advances in the understanding of sensory signals recorded with nerve cuffs have led to their consideration as sources of feedback for the control of closed-loop functional electrical stimulation (FES) systems as described in Hoffer, U.S. Pat. No. 4,750,499 entitled CLOSED-LOOP, IMPLANTED-SENSOR, FUNCTIONAL ELECTRICAL STIMULATION SYSTEM FOR PARTIAL RESTORATION OF MOTOR FUNCTIONS.